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Controlling 6 steppers for Orrery Answered

I'm currently designing an orrery planetarium and my current mechanical geared design is rather dense (See attached images) takes up a lot of space, and would involve a lot of gear fabrication.

So I'm wondering if I can use 6 stepper motors to run the system and do the ratios in code. If it helps reduce the cost, size, and adds more control options (like inputting a specific date and having the planets move to it) it could be worth consideration.

I'm just currently unsure of the best way to control 6 steppers. I'm looking into an Arduino Mega for starters, but I'm not sure how much I/O I can get away with. I plan to just do tests with one motor at a time until I've got six running.

The good news is the inner orbits are a smaller diameter involving fewer rotations per orbit and while the outer rings are larger and although they require more rotations per orbit, they move much slower. I can probably find a way to add limit switches if necessary and the I/O allows it, which might be nice for calibration. I don't see this as something I'll be running all the time, since I could see it needing a power supply and long term continuous operation may not be possible with the motors. I'd be open to using servos instead if they could use fewer I/O pins and still rotate continuously, but I'm still doing research.

I'm open to any suggestions, ideas, or criticisms for this approach and any assistance is appreciated.

For now, I'm still in gear land.